Tractor-to-trailer air brake lines and trailer slider lines are always used in pairs with two separate lines extending substantially parallel to one another. The first line is for service braking, i.e., braking which is normally relied on, and the second line is an emergency air brake line. It is the current practice to have two separate brake lines which are held in proximity to one another with clips, tethers or brackets.
Truck trailers with long beds present an additional problem because these trailers are frequently equipped with rear axles that are slidably adjustable to move in forward and rearward directions with respect to the beds. It is necessary to have axles which are adjustable in this manner because truck trailers carry loads of various sizes which may have horizontal centers of gravity which are closer to one end of a trailer bed than the other. During the past 15 years, regulations have changed, allowing truck trailers of increased length. Such truck trailers almost necessarily must have rear axles which are slidable fore and aft.
In order to properly stop tractor trailers, it is necessary to brake the wheels of the slidable rear axle or axles, as well as the tractor wheels. Generally, activation of the wheels of slidable rear axles is accomplished by pairs of hoses which are configured as coil tubes, the coils of which expand and contract as the rear axles are moved fore and aft on the trailer bed.
Since coiled tubes require considerably more tube length to connect between locations than uncoiled tubes, the expense of coiled tubes is considerably higher than the expense of uncoiled tubes. It is, however, difficult to keep pairs of air brake tubes proximate one another if the tubes are not nested, as in the case of coiled tubes, or if the tubes are not held together by tethers, clamps or brackets, which are also expensive as well as being otherwise troublesome.